Seat suspension system

ABSTRACT

A seat suspension system for a vehicle and including a seat attached to a seat support. The seat support is supported for movement through links on a frame attached to the vehicle. The seat suspension system includes stabilizing means in the form of a pair of coil springs having one end attached to the frame and the other end attached to the seat support with the ends of the springs limited for rotational movement only so that the effective spring force per increment of seat displacement increases non-linearly relative to the displacement of the seat support. The stabilizing means further includes a pair of shock absorbers which are positioned between the frame and the seat support and are attached in a manner that the shock absorbers will be substantially fully retracted in the normal ride position of an operator. The seat suspension system further includes interconnecting mechanism between the seat and seat support which accommodate movement in four directions from a central position.

United States Paten Stannebein [54] SEAT SUSPENSION SYSTEM [72]Inventor: Clifford E. Stannebein, Brooklyn Center, Minn.

[73] Assignee: J. 1. Case Company [22] Filed: Oct. 30, 1969 [21] Appl.No.: 872,607

[52] US. Cl ..248/399, 248/430 [51] Int. Cl ..A47c 3/22 [58] Field ofSearch ..248/399, 430, 429, 376, 373, 248/374, 400, 372

[56] References Cited UNITED STATES PATENTS 2,104,511 1/1938 Faulhaber..248/373 2,414,954 1/1947 Kalter, ....248/374 2,714,001 7/ 1955 Herseyet a1 ..248/400 2,742,952 4/ 1956 Bellamy .;....248/430 2,850,073 9/ l95 8 Smith ..248/430 2,875,810 3/1959 Simons et a1. ..248/400 2,917,35012/ 1959 Ragsdale ..248/430 2,986,199 5/1961 Ferreira et al ..248/3993,109,621 Ill 1963 Simons et a1. ..248/399 3,244,393 4/1966 Wallerstein,Jr ..248/430 849,975 4/1907 Carlson ..248/372 Aug. 22, 1972 PrimaryExaminer-Edward C. Allen Attorney-Messier, Goldsmith, Clement & Gordon57 ABSTRACT A seat suspension system for a vehicle and including aplacement of the seat support. The stabilizing means further includes apair of shock absorbers which are 1 positioned between the frame and theseat support and are attached in a manner'that the shock absorbers willbe substantially fully retracted in the normal ride position of anoperator.

The seat suspension system further includes interconnecting mechanismbetween the seat and seat support which accommodate movement in fourdirections from acentral position.

15 Claims, 5 Drawing Figures 3.685.780 sum 1 or 4 PHENTEB 1:22 1972FORCE LBS PATENTED ms 22 m2 SHL'EI Q 0F 4 LARGE cou. SPRINGS m TORSION(4.91 |N-LBS/DEG.)

/L|NEAR S-PRING FOR I65). MAN

RIDE POSITION I I l I O I 2 3 4 I 5 DEFLECTION IN INCHES m/ws/vroe07'7'0PA/F/5 1 SEAT SUSPENSION SYSTEM BACKGROUND OF THE INVENTION Thepresent invention relates generally to seat suspension systems and moreparticularly to a seat suspension system for heavy duty off-the-highwayequipment.

In recent years, the matter of operator comfort has received anincreasing amount of attention by manufacturers of heavy duty equipment,particularly farm equipment such as tractors, self-propelled combinesand the like. This continuing interest has been directed towardsproviding increased seating comfort in the form of fully adjustable seatsuspension systems to improve the riding qualities for the operator.

One type of arrangement which has found considerable commercial successis a seat suspension system which incorporates links which support theseat at one end and which are pivoted to a frame at the opposite end sothat the seat may swing downwardly under the weight of the operator. Thedownward movement of the seat is resisted by some sort of springarrangement which will impart a force tending to return the seat to itsfirst or rest position. Some of these seat suspension systems alsoincorporate shock absorbers which further tend to resist the downwardmovement of the seat particularly whena sudden jar is encountered, aswhen the vehicle travels over rough terrain.

While such a seat arrangement has been used on many types of vehicles,there are several inherent disadvantages which are annoying to theoperator.

One of the problems of heretofore known seat suspension systems is thatthe spring force applied to the seat was normally in the form of aconstant force from a spring, such as a coil spring, arranged end to endbetween the seat and the frame. Such an arrangement is disclosed inMorrison et al. US. Pat. No. 2,954,071.

The inherent disadvantage of an arrangement of this type is that anequal amount of force is applied during each increment of displacementof the seat relative to the frame.

Also, in order to prevent bottoming out it was heretofore considerednecessary in a coil spring arrangement of the type disclosed in theMorrison et al. patent to also incorporate heavy shock absorbers whichwere axially disposed between the frame and the seat support andprovided a dampening force during the entire extent of movement of theseat. Thus, if the vehicle were operated in rough terrain and a suddenupward movement of the frame were encountered, the shock absorbers couldnot accommodate this sudden movement to maintain the seat tion.

Also, with such an arrangement, shock absorbers would not react withsufficient speed to accommodate a sudden downward movement of the frameresulting in having the seat move downwardly and leaving the operatorsuspended in mid-air. Stated another way, in order for the seat to movein either direction from the normal ride position, the shock absorbersin heretofore known seat constructions would have to be extended orretracted.

A further problem of the suspension system of the type referred toabove, is that no provision is made for lateral shifting of the seatwhen the vehicle is transversely or longitudinally tilted. While priorproposals have at a predetermined ride posibeenv made to overcome thisproblem, such prior proposals have not come into general usage to anysubstantial extent for they either have been too complex and/or couldonly be incorporated into certain types of seat constructions.

BRIEF SUMMARY OF THE INVENTION The presentinvention provides an improvedstabilizing mechanism for a seat support and seat that is supported byparallel spaced links from a frame. The stabilizing means is in the formof a pair of axially aligned coil springs which are fixed in axiallength and which have one end connected to the frame and the oppositeend rotatable in response to displacement of the seat relative to theframe. The springs are arranged to produce an effective force which isnon-linear relative to the displacement of the seat and moreparticularly the spring force varies exponentially relative to thedeflection of the seat from the rest or raised position.

The stabilizing means further includes mechanism for adjusting theprestress of the springs when the seat is in the rest or first position.The stabilizing means further includes a pair of shock absorbers whichare specifically positioned .so that they will not dampen smalldisplacements of the seat and support from its normal ride position.

According to a further aspect of the present invention, the vehicle seatsuspension system further includes mechanism for isolating the seat fromrelative displacements of the frame and the vehicle a in the horizontalplane. This arrangement is particularly important to prevent any suddentransverse movement of the operator when the vehicle is suddenly tiltedtransversely to the longitudinal axis or rapidly pivoted about the mainaxle of the tractor. The particular mechanism for isolation includesfirst and second pairs of perpendicularly disposed rail means each ofwhich includes a first rail element fixed to the seat support and asecond rail element fixed to the seat with antifriction means interposedbetween each of the first and second rail elements. The mechanismfurther includes resilient means or springs which tend to maintain theseat in a central position relative to the seat support but which willaccommodate movement of the seat in four directions from the centralposition.

Thus, the vehicle seat suspension system substantially isolates the seatfrom vehicle displacement in transverse and longitudinal directions inthe horizontal plane as well as vehicle displacement in the vertical,

7 plane and the spring force applied to the seat increases for eachincrement of seat displacement beyond the ride position and approachesinfinity so that what is commonly called bottoming ,out' is virtuallyeliminated.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS seat isunoccupied.

- FIG. 4 is a vertical sectional view'ta ken generally.

along lines 4-4 of FIG. 2; and

1 FIG. 5 is a graph showing the spring force inpounds verses seatdeflection in inches. I 1 I DETAILED DESCRIPTION I While the inventionis susceptible of embodiment in many different forms, there is showninfthe drawings and will herein be described in detail one specific embodiment, with the understanding that the present dis-.

closure is to be considered asan exem'plification of the principles ofthe invention and is not intended to limit the invention to theembodiment illustrated.

. FIG. 1 of thedrawings discloses a seat suspension system forsupporting a seat'l2on a frame 14 which forms partof a vehicle (notshown); The seatisuspension system includes an attachment'structure orseat U frame 14 by linkage "including. first second parallel pairszoflinks 18. Each link is pivotedat qns 'i still and he Op n pivoted at 22on ftheseat support, The four links-l8 thus cooperate to define a;parallelogram type linkage for'suspending the seat supportandseat on thy f meswas indicatedtabove, it is customaryto provide sorne-;typeofstabilizing for resisting the support 16'supported for displacementrelative to the 4 grasped by an operator for rotation of the rod. Inorder to allow rotational movement of the plate 34 on the pivot axis 35,the lug or member 37 extendsthrough a circumferential slot 54 fonnedinone of the members 36 so as to accommodate such rotational movement. It

should be noted that the rotational axis for the plate 34; defined bybolt 35, is disposed on the'axis of the respec- I tive springs which arein alignment with each -other.- I Thus, the adjacent ends 32of thesprings are rotated about the pivot on a common radius.

The means for connecting the second or outer ends 33 of the respectivecoil springs to the seat support are identical in construction and onlyone will be described. The second means includes a shell or member 60(FIGS. 2 and 3) rotatably joumaledon a lug or member 62 extendingupwardly from'the base of theframe 14. The member or hub 60 has itsrotational axis' defined by bolt 64 which is l ocated'on the common axisof the respective springs 30, for a purpose which-will beoome'apparenthereinaft r.-

' suitable bearing may be interposed between the bolt64 and the "memberendsfof downward movement of the'seatrelative to the frame andwhichjmaintains the seat support or attachment structure as well as theseat in a first position when the According to .the present invention,the stabilizing means (FIG. 2) includes first and second coil springs 30each having one. end 32'connected-to the frame and the opposite end 33connected to the attachment structure or seat support. The means forconnecting one end 32 of each of the coil springs to the frame includesa plate the respective springs 30 are connected to therespectivemembers'60 through'a'bolt 68 -receiving a spacer or sleeve 70and a washer freeendofthebolt;

The sec nd 01": respectively I connecting .the opposite ends of therespective springs to the seat-support each further include an 72extending radially from the member 60 and rigidly connected thereto, as

by welding. The free end of the arm is pivotally connected to one end ofa link 74 through a bolt 76. The

or element 34 rotatably supported on 'a pivot axis 3 defined by a bolt35 on a lug 37 extendingupwa'rdly from thebase of the frame 14. Theplate 34 has a pair of circular members 36 extending from opposite sidesthereof and respectively receiving the ends 32 of the respective [coilsprings 30. The connection between the ends'of the respective coilsprings and the plate-includes a sleeve or spacer 39 received on a bolt40 ;with"washers 41 maintaining the ends 32' of the 34. Thus, tighteningof the nut on the bolt 40 will simultaneously fixedly secure theadjacent ends of the respective coil springs to the plate.

According to another aspect of the present invention,'the connectionmeans between the frame and the the positionof the ends oftl'lerespective coil springs to springs on the sleeves and in engagementwith the plate coil springs includes adjustment means for changing athereby vary the prestressed condition of he springs when theseatsupportor attachment'structure is in the rest or first position. The adjustingmeans or mechanism includes an elongated rod (FIGS. 2 and 4) 42 having athreaded end received in a floating nut 44 7 carried by a supportextending between a pair of spaced plates 48 respectively secured to theplate 34 and one of the circular members 36. v v end of the rod 42 isrotatably jo'umaled ally fixed relative to the support member 50. Thefree i end of the rod 42 has a knob 52 which is adapted to be inasupport so forming part of the frame 14 and is axiopposite end of thelink 74 is likewise pivotally con'-" of each of the coil springs are ina single Y plane which extends transversely ofaxisjof the springso, thatthe opposite ends of the springs are limited to rotation about the axis.Also; the longitudinal axes of the links 72 and 74 aresubstan'tiallyfperpeni dicular when theseat is in the rest'positionshown in.

FIG. 1 and the movement of link 74 is substantially tangentially of theaxis of rotation of the spring 30.I-Iowever, in the normal ride positionthe links are at an acute angle and the movement of the'link 74 willextend chordally of the axis of rotation of the spring 30. Thisarrangement, results in substantially equal spring force per incrementof seat displacement between the rest and ride positions and anincreased spring force for each increment of displacement of the seat 12and seat a support 16 beyond the ride position. The relationship ofspring force and deflection or displacementof the I seat from the restposition is graphically illustrated in FIG. 5. The deflection orseat'displaceme'nt is charted J in inches while the force of the springin pounds. It will benoted that during the-.original-incre ments ofmovement of the seat from the rest position, the spring forceperincremcnt of movement will remain substantially constant to a point justbeyond the .71 ,received'on the I oftheseatl2and ride position for anormal man selected as a man of approximately 165 pounds weight plustheweight of the seat support and seat. Beyond the normal ride position ofthe operator, the spring force-deflection curve rises sharply andapproaches infinity. Thus, it will be seen that the spring force variesexponentially with respect to displacement of the seat beyond the rideposition. This particular arrangement is of extreme importance inproviding an increased force to the seat as the seat is deflectedfurther downwardly than the normal ride position to prevent bottomingout and still utilize spring force during all portions of movement ofthe seat support and seat relative to the frame.

According to another aspect of the invention, the stabilizing means alsoincludes a pair of shock absorbers which are positioned in a manner thatno dampening force is produced by the shockabsorbers when the seat is inthe normal ride position. The shock absorbers are more clearly shown inFIGS. 2 and 4 and each include a cylinder 90 and a piston 'rod92-whichdefine relatively movable elements with the piston rod 92 beingextensible and retractable relative to the cylinder 90. Each cylinder 90has a collar 94 at one end thereof which is attached through bolts 97 toa bracket 96 extending vertically from the bottom of the frame 14. Thebrackets 96 are in the form of channel members having a plurality ofsets of aligned openings 98 in the respective legs of the channels witheach set of openings adapted to receive the bolt for connecting thecylinder 90 to the bracket 96. Thus, the position of the free or headend of the cylinder may be vertically adjustable by appropriateselection of the openings 98.

The free end of the second movable element or piston rod 92 is connectedto the seat support or attachment structure through a collar 100received between a pair of plates 102 which have openings to receive abolt 104. Suitable bearings or antifriction means 106 may be interposedbetween the plates and the collar 100.

The selection of the set of openings 98 to be utilized for theconnection of the cylinder to the bracket- 96 is determined by theweight of the normal operator for the vehicle. Thus, for a relativelylight operator, the upper set of openings 98 would be utilized while,with a very heavy operator, the lower set of openings .would beutilized. The cylinder connection to the bracket is made so that duringthe normal ride position of the seat and seat support, the respectiveshock absorbers are in a substantially horizontal plane spaced below thehorizontal plane defined by the seat 12 and extend perpendicular to thedirection of movement of the seat. In this position, the relativelyextensible and retractable elements 90 and 92 are in a substantiallyfully retracted position and will be required to be extended relativeto. each other when the seat support is moved in either direction fromthe normal ride position. This particular arrangement is of extremeadvantage in providing a seat stabilizing mechanism which is capable ofrapidly reacting to any sudden relative movement between the frame andthe seat support in either direction from the ride position. Thearrangement of the shock absorbers in this manner will have only thespring force acting on the seat support when the operator is in thenormal ride position. It will be appreciated that the coil springs willvery rapidly react to any. small displacement of the seat directionswith the movement being resisted by resilent means and tending tomaintain the seat in a central position. The resilient means has anincreasing force as the seat moves from the central position to therebyprevent any sudden transverse movement or longitudinal movement of theseat relative to the seat support.

The mechanism between the seat and seat support includes a firstand-second pairs of rails 110 which extend perpendicular to each otherand are spaced from each other. Each rail 110 includes similarly shapedand constructed first and second rail elements with'antifriction meansin the form-of roller bearings 122 interposed to allow longitudinalmovement of the rail elements relative to each other. The first pair ofrail elements (FIG. 2) includes a first rail element 112 fixed to theseat through a bracket 114 and bolts 116.

The first pair of rails 110 also each include a second rail element 118,with the second rail elements of the first pair of rails fixed to thefirst rail element 112 of the second pair of rails (FIG. 1) as bywelding. The second rail elements 118 of the second pair of rails aresecured to the seat support 16 through brackets 120 and 132.

The mechanism for maintaining the seat in a central position relative tothe seat support comprises two sets of springs 126 and 127 each havingone end connected to the seat support and having the opposite endconnected to the seat. The connection between the springs and the seatincludes a transversely extending rail member 128 fixed to the seatthrough suitable support mechanism 130 so as to move with the seat. Theopposite ends of the two sets of springs 126 and 127 are respectivelyconnected to brackets 131 and 132 which are carried by the seat support.

The respective sets of springs 126 and 127 are each arranged in twogroups angularly related to each other (see FIG. 2) and will tend tomaintain the seat in a transverse central position. As the seat is movedtransversely in either direction, as viewed in FIG. 2, one-half of eachgroup of springs will produce an increased force tending to move theseat back to its centered position while the other half of each group ofsprings will have adecreased force which will further tend to allow theseat to the centered position. When the seat is .moved fore and aft ofthe vehicle or left and right as viewed in FIG. 1 along the second groupof rails, one group of springs, will produce an increased spring forcetending to center the seat while the second group of springs willproduce a decreased centering force.

The particular arrangement of the springs and the rails will tend tomaintain the seat in a centered position on each of the rails or railmeans and will guide the seat for movement in opposite directions fromthe centered position with the resilient means accommodating themovement in response to sudden movement of the seat supportrelative tothe seatto thereby'partially isolate the seat from-the seat support.

It should be noted, that the particular arrangement of the rails as'wellas the biasing means will allow movement of theseat in four directionsfrom the centered position. Such movement in four directions willthereby accommodate any sudden pivotal movement of the vehicle about thetransversely extending main axle or any pivoting of the vehicle andframe relative to its longitudinal axis. Thus, the particular attachmentbetween the seat. and seat support will allow the operator to .rernainina substantially centered position and the springs will prevent anysudden transverse movement fof the seat relative to the frame which,inextreme cases, couldthrow theoperator from the seat. As will beappreciated, the particular arrangement of t the seat suspension meanswill substantially completely isolatethe operator from movement of theframe relative to seat in either the horizontal or the vertical saidmechanism further includes and second rails i direction. Furthermore,the specific arrangement of the v springs produce an increased springforce for each increment of-movementbeyond the normalride positionmechanism, the shock absorbers are mounted in they appropriate positionto be in a horizontal frame when the operator ,is seated thereon; theentire mechanism operates automatically'without any additional attentionof, the operator. Furthermore, if the vehicle is to be operated forsubstantial periods of time by an operator having different weights, itis only necessary to reposition the shock absorbers so that they willbe'in thehorizontal positionwhen the heavier or lighter operator issupported on the seat. 1 What is claimed is: 1

1 In combination with a vehicle seat supported on a seat attachmentstructure in a substantially horizontal to said attachment structure,

being located below the axis of said spring and the included anglebetween said arm and said link being less than 90 in the ride positionso that displacement or said attachment structure beyond the ridepositionwill cause said spring to produce a force which is non-linear"and which increases substantially exponentially to the displacement ofsaid oppositeend.

2. The combination as'defrned in claim 1, including 3 the furtherimprovement of mechanism for attaching said seat to said attachmentstructure, said, mechanism accommodating movement'of said seat inopposite. directions from a central position, saidmover'nent being alongsubstantially perpendicular axes in said" horizontal plane, .saidmechanism including resilient means tending to maintain said seat insaid central position; r y

3. The combination as defined in claim 2, in which extendingperpendicular to each other, railsIeach including first and second railelements,said first ele-, mentof said first rail'being connected to saidseat and said second element of second rail being attached 4. Thecombination as defined in .claim 3, including the further improvementofantifriction means interposed between each of said first and second railelements. 7

plane,-a vehicle seat suspension comprising a frame;

linkage means suspending said attachment structure on said frame; andstabilizing means tending to maintain said attachment structure in arest position, said stabilizing means-comprising a coil spring having anaxis extending substantially parallel to said horizontal plane; firstmeans connecting .one' end'of said coil spring to said frame; and secondmeans connecting an opposite end of said coil spring to said attachmentstructure in a manner to rotate said opposite end-about said axis as afunction of the movement of said attachment structure from the restposition to a ride position, said second means including a rigid armconnected to said opposite end of said spring and extending transverselyof the axis of said spring, and a rigid elongate link pivotallyconnected atone end'to said attachment structure and pivotally.connected at its opposite end to said arm, said arm being located abovethe axis of spring and the included angle between said arm and said linkbeing at least 90 when said attachment structure is in the restposition, and said arm 5. The combination as defined in claim r, inwhich said first means includes an element rotatable on said frame abouttheaxis of said spring, saidone end of said spring having a connectionto said element at a point spaced from said axis, and means forrotatingsaid ele- 1 ment to adjust the prestr'e ss condition for said spring.

6. The combination as defined in claim 1, in which said second meanscomprises a member for rotation only on said frame with said oppositeend of said spring and said arm connected to said member.

' 7. The combination as defined in claim 1, including the furtherimprovement of a shock absorber having first and second extensible andretractable elements, one of said elements connected to said frame andthe otherof said elements connectedto attachment structure, said shockabsorber being positioned to have said elements in a retracted positionwhen said seat attachment structure is in a ride position for anoperator whereby said shock absorber elements must be extended relativeto each other when the seat attachment structure is moved in eitherdirection from said ride position. I

8. In combination, a seat support, a seat mounted onv said seat supportina substantially horizontal plane and facing in a direction of travel;a frame; linkage means c suspending said seat support for verticalmovement relativeto said frame; stabilizing means for said seat and seatsupport comprising biasing means interposed between said seat supportand said frame; and a pair of shock absorbers having first and secondextensible and retractable elements respectively pivotally connected tosaid frame and seat support, said shock absorbers being positioned onopposite sidesof, the centerline of said seat. support and extendingtransversely I H with respect to said direction of travel of said seat,f v V shockabsorbers being upwardly inclined between said frame and seatsupport in the rest position; and means defining a plurality ofconnection positions for one element of each shock absorber so that theelements may be connected at selected positions, depending upon theweight of the occupant of the seat, to locate the elements of each shockabsorber in a substantially fully mal ride position.

9. In a vehicle seat suspension having a seat support; a seat; and meansmounting said seat on said seat support, the improvement of said meanscomprising first longitudinal rail means extending generally fore andaft of said seat; second longitudinal rail means extending generallytransversely of said seat, each of said rail means having a pair of railelements, one rail element of each rail means being respectivelyconnected to said seat and said seat support, the second rail elementsbeing interconnected; and resilient means for maintaining said seat in acentered position on each of said rail means, said resilient meansincluding first and second spring means each having one end connected tosaid seat and an opposite end connected to said seat support,-said firstand second spring means converging upwardly from the point of connectionto the seat support to the point of connection to the seat, saidresilient means further including third and fourth spring means eachhaving one end connected to said seat and an opposite end connected tosaid seat support, said third and fourth spring means conveying upwardlyfrom the point of connection to the seat support to the point ofconnection to the seat, said rail means guiding said seat for movementin opposite directions from said centered position with said resilientmeans accommodating said movement in response to sudden movement of saidseat support whereby to partially isolate said seat from said seatsupport.

10. A vehicle seat suspension as defined in claim 9, including thefurther improvement of a frame adapted to be supported on a vehicle;linkage means supporting said seat support for movement relative to saidframe; and stabilizing means for said seat support; said stabilizingmeans including a coil spring having one end secured to said frame andthe opposite'end connected to said seat support; and means formaintaining the opposite ends of said coil spring in planes extendingtransversely of the axis of said spring whereby the opposite end of saidspring is limited to rotation about said axis and arranged to produce anon-linear force on said seat support when said seat is moved from afirst position.

11. A vehicle seat suspension as defined in claim 10, including thefurther improvement of said stabilizing means including a shock absorberhaving a first element connected to said frame and a second elementconnected to said seat support, said shock absorbers being positioned tohave said elements in a fully retracted position when said seat is in aride position of an operator supported thereon.

12. In combination with a frame having a seat support with a seatattached thereto and linkage means including first and second verticallyspaced pairs oflinks each having one end pivotally connected to theframe and the opposite end pivotally connected to said seat support;stabilizing means for said seat and seat support 582833631 'tll ix oifiifilgi'fizi dfig iil'isely of said links; first means connecting theadjacent ends of said springs tosaid frame; and second means connectingthe remote ends of said springs to said seat support, said second meansincluding a radially extending rigid arm connected to the remote end ofeach of said springs and interconnecting means cooperating with saidarms for rotating said arms as a function of seat support displacement,said interconnecting means each being defined by a rigid elongate linkpivotally connected at one end to said seat support and'pivotallyconnected at its opposite end to one of said arms, said arms beinglocated above the axes of said springs and the included angle betweensaid arms and said links being at least 90 when the seat is in a firstposition, and said arms being located below the axes of said springs andthe included angle between said arms and said links being less than 90so that displacement of the seat sup port beyond the ride position willcause said springs to produce a force which is non-linear and whichincreases substantially exponentially to the displacement of said remoteends when said seat is in a ride position.

13. The combination as defined in claim 12, in which said first meansincludes a lug extending from said frame and disposed between saidadjacent ends of said springs and a plate rotatable on said lug aboutthe axes of said springs with said adjacent ends connected to saidplate; and said second means includes first and second members rotatableabout said axes with said arms connected to said members.

14. The combination as defined'in claim 12, in which said stabilizingmeans further includes first and second shock absorbers each havingextensible and retractable elements respectively attached to said frameand said seat support, said shock absorbers being in fully retractedcondition when said seat support and seat are in a normal ride positionfor an operator.

15. The combination as defined in claim 12, including the furtherimprovement of means accommodating relative movement between said seatand seat support and comprising first and second pairs ofparallel railsv each having first and second rail elements, said first rail elementsof said first rails being connected to said seat and said second railelements of said second rails being connected to said seat support, saidfirst and second pairs of rails extending substantially perpendicular toeach other; roller means between said first and second rail elements;and biasing means normally maintaining said seat in a central positionrelative to said seat support, said biasing means accommodating movementof said seat in any one of four directions from said central position inresponse to sudden movement of said seat support.

1. In combination with a vehicle seat supported on a seat attachmentstructure in a substantially horizontal plane, a vehicle seat suspensioncomprising a frame; linkage means suspending said attachment structureon said frame; and stabilizing means tending to maintain said attachmentstructure in a rest position, said stabilizing means comprising a coilspring having an axis extending substantially parallel to saidhorizontal plane; first means connecting one end of said coil spring tosaid frame; and second means connecting an opposite end of said coilspring to said attachment structure in a manner to rotate said oppositeend about said axis as a function of the movement of said attachmentstructure from the rest position to a ride position, said second meansincluding a rigid arm connected to said opposite end of said spring andextending transversely of the axis of said spring, and a rigid elongatelink pivotally connected at one end to said attachment structure andpivotally connected at its opposite end to said arm, said arm beinglocated above the axis of said spring and the included angle betweensaid arm and said link being at least 90* when said attachment structureis in the rest position, and said arm being located below the axis ofsaid spring and the included angle between said arm and said link beingless than 90* in the ride position so that displacement of saidattachment structure beyond the ride position will cause said spring toproduce a force which is nonlinear and which increases substantiallyexponentially to the displacement of said opposite end.
 2. Thecombination as defined in claim 1, including the further improvement ofmechanism for attaching said seat to said attachment structure, saidmechanism accommodating movement of said seat in opposite directionsfrom a central position, said movement being along substantiallyperpendicular axes in said horizontal plane, said mechanism includingresilient means tending to maintain said seat in said central position.3. The combination as defined in claim 2, in which said mechanismfurther includes first and second rails extending perpendicular to eachother, said rails each including first and second rail elements, saidfirst element of said first rail being connected to said seat and saidsecond element of said second rail being attached to said attachmentstructure.
 4. The combination as defined in claim 3, including thefurther improvement of antifriction means interposed between each ofsaid first and second rail elements.
 5. The combination as defined inclaim 1, in which said first means includes an element rotatable on saidframe about the axis of said spring, said one end of said spring havinga connection to said element at a point spaced from said axis, and meansfor rotating said element to adjust the prestress condition for saidspring.
 6. The combination as defined in claim 1, in which said secondmeans comprises a member mounted for rotation only on said frame withsaid opposite end of said spring and said arm connected to said member.7. The combination as defined in claim 1, including the furtherimprovement of a shock absorber having first and second extensible andretractable elements, one of said elements connected to said frame andthe other of said elements connected to said attachment structure, saidshock absorber being positioned to have said elements in a retractedposition when said seat attachment structure is in a ride position foran operator whereby said shock absorber elements must be extendedrelative to each other when the seat attachment structure is moved ineither direction from said ride position.
 8. In combination, a seatsupport, a seat mounted on said seat support in a substantiallyhorizontal plane and facing in a direction of travel; a frame; linkagemeans suspending said seat support for vertical movement relative tosaid frame; stabilizing means for said seat and seat support cOmprisingbiasing means interposed between said seat support and said frame; and apair of shock absorbers having first and second extensible andretractable elements respectively pivotally connected to said frame andsaid seat support, said shock absorbers being positioned on oppositesides of the centerline of said seat support and extending transverselywith respect to said direction of travel of said seat, said shockabsorbers being upwardly inclined between said frame and seat support inthe rest position; and means defining a plurality of connectionpositions for one element of each shock absorber so that the elementsmay be connected at selected positions, depending upon the weight of theoccupant of the seat, to locate the elements of each shock absorber in asubstantially fully retracted, substantially horizontal position whensaid seat support and said seat are in a normal ride position wherebysaid elements must be extended when said seat support is moved in eitherdirection from the normal ride position.
 9. In a vehicle seat suspensionhaving a seat support; a seat; and means mounting said seat on said seatsupport, the improvement of said means comprising first longitudinalrail means extending generally fore and aft of said seat; secondlongitudinal rail means extending generally transversely of said seat,each of said rail means having a pair of rail elements, one rail elementof each rail means being respectively connected to said seat and saidseat support, the second rail elements being interconnected; andresilient means for maintaining said seat in a centered position on eachof said rail means, said resilient means including first and secondspring means each having one end connected to said seat and an oppositeend connected to said seat support, said first and second spring meansconverging upwardly from the point of connection to the seat support tothe point of connection to the seat, said resilient means furtherincluding third and fourth spring means each having one end connected tosaid seat and an opposite end connected to said seat support, said thirdand fourth spring means conveying upwardly from the point of connectionto the seat support to the point of connection to the seat, said railmeans guiding said seat for movement in opposite directions from saidcentered position with said resilient means accommodating said movementin response to sudden movement of said seat support whereby to partiallyisolate said seat from said seat support.
 10. A vehicle seat suspensionas defined in claim 9, including the further improvement of a frameadapted to be supported on a vehicle; linkage means supporting said seatsupport for movement relative to said frame; and stabilizing means forsaid seat support; said stabilizing means including a coil spring havingone end secured to said frame and the opposite end connected to saidseat support; and means for maintaining the opposite ends of said coilspring in planes extending transversely of the axis of said springwhereby the opposite end of said spring is limited to rotation aboutsaid axis and arranged to produce a non-linear force on said seatsupport when said seat is moved from a first position.
 11. A vehicleseat suspension as defined in claim 10, including the furtherimprovement of said stabilizing means including a shock absorber havinga first element connected to said frame and a second element connectedto said seat support, said shock absorbers being positioned to have saidelements in a fully retracted position when said seat is in a rideposition of an operator supported thereon.
 12. In combination with aframe having a seat support with a seat attached thereto and linkagemeans including first and second vertically spaced pairs of links eachhaving one end pivotally connected to the frame and the opposite endpivotally connected to said seat support; stabilizing means for saidseat and seat support comprising: first and second coil springs locatedend-to-end with the axes of said spriNgs extending transversely of saidlinks; first means connecting the adjacent ends of said springs to saidframe; and second means connecting the remote ends of said springs tosaid seat support, said second means including a radially extendingrigid arm connected to the remote end of each of said springs andinterconnecting means cooperating with said arms for rotating said armsas a function of seat support displacement, said interconnecting meanseach being defined by a rigid elongate link pivotally connected at oneend to said seat support and pivotally connected at its opposite end toone of said arms, said arms being located above the axes of said springsand the included angle between said arms and said links being at least90* when the seat is in a first position, and said arms being locatedbelow the axes of said springs and the included angle between said armsand said links being less than 90* so that displacement of the seatsupport beyond the ride position will cause said springs to produce aforce which is non-linear and which increases substantiallyexponentially to the displacement of said remote ends when said seat isin a ride position.
 13. The combination as defined in claim 12, in whichsaid first means includes a lug extending from said frame and disposedbetween said adjacent ends of said springs and a plate rotatable on saidlug about the axes of said springs with said adjacent ends connected tosaid plate; and said second means includes first and second membersrotatable about said axes with said arms connected to said members. 14.The combination as defined in claim 12, in which said stabilizing meansfurther includes first and second shock absorbers each having extensibleand retractable elements respectively attached to said frame and saidseat support, said shock absorbers being in fully retracted conditionwhen said seat support and seat are in a normal ride position for anoperator.
 15. The combination as defined in claim 12, including thefurther improvement of means accommodating relative movement betweensaid seat and seat support and comprising first and second pairs ofparallel rails each having first and second rail elements, said firstrail elements of said first rails being connected to said seat and saidsecond rail elements of said second rails being connected to said seatsupport, said first and second pairs of rails extending substantiallyperpendicular to each other; roller means between said first and secondrail elements; and biasing means normally maintaining said seat in acentral position relative to said seat support, said biasing meansaccommodating movement of said seat in any one of four directions fromsaid central position in response to sudden movement of said seatsupport.